Conventional EPRs are elastomeric polymers used in such applications as single ply roofing, hose and tubing, wire and cable, automotive weatherstripping, and gaskets. They are generally formulated with fillers, oils, processing aids, and stabilizing agents, and can be cured with organic peroxides such as dicumyl peroxide or by reacting the EPDMs with sulfur in the presence of accelerators. Commercially available EPRs require vulcanization to produce desirable mechanical properties suitable for practical use. These EPRs have relatively low crystalline contents and have relatively low melting points, e.g., melting points in the 40.degree. C. to 60.degree. C. range, which make them unsuitable for use at elevated temperatures without crosslinking. In order to improve unvulcanized mechanical properties, the EPRs are often blended with thermoplastics such as polyethylene or polypropylene.
Thermoplastic elastomers bear a resemblance to EPRs in that they are rubbery materials. A unique characteristic of thermoplastic elastomers is that they can be thermoformed by techniques generally associated with thermoplastic resins. Thermoplastic elastomers normally contain elastomeric domains and crystalline or partially crystalline thermoplastic domains. The elastomeric phase lends rubbery properties, while the relatively hard thermoplastic phase provides strength below the melting point of the thermoplastic elastomer and good processability above the melting point. When the elastomeric phase is crosslinked, the method of crosslinking must be selective to the elastomer so as to avoid crosslinking the thermoplastic phase, and thus retain its beneficial processability.
It would be advantageous to be able to provide a polymer, whether a polyethylene or an EPR, which does not have to be crosslinked yet exhibits the desirable physical properties of crosslinked thermoplastic elastomers including high strength over a wide range of use temperatures and shows good processability over a wide range of processing temperatures.